Under conditions of usual outside temperatures heavy oils and extra-heavy oils can be transported in pipelines only with difficulty because of their very high viscosity. Therefore, to increase their mobility they are often mixed with low-viscosity crude oils or refinery cuts; such a mode of operation requires relatively great quantities of additives to achieve an appreciable improvement in flow. Moreover, such a procedure is efficient only where light-oil fields exist in the same locality or a nearby refinery is able to deliver low-viscosity gasoline fractions.
Another method also used consists in feeding heat to the heavy oil to lower its viscosity and correspondingly to improve its flow; for which considerable amounts of heat must be expended. Thus, it is necessary, e.g., to heat a heavy oil of 10.3.degree. API, whose viscosity at 20.degree. C. is 40,000 mPa to a temperature of about 95.degree. C. to attain a viscosity of about 100 mPa, a threshold value often required for oil transportation in pipelines (M. L. Chirinos et al., Rev. Tec. Intevep. 3 (2):103 [1983]). This requires a high expenditure for equipping and maintaining the pipelines, and a loss of 15 to 20% in crude oil, since the necessary amount of heat is usually obtained by combustion of crude oil.
Another method for heavy oil transport resides in pumping the oil through the pipelines in a more or less readily fluid emulsion. Since the viscosity of emulsions is determined predominantly by the dispersing agent, here an oil-in-water emulsion is involved. The oil-in-water emulsion is obtained by adding water and emulsifier to the oil using shear forces. This mixture is then pumped into the pipeline. In a settling tank, the emulsion is again separated into oil and water and the separated oil is fed to the refinery. The emulsifier should, in as small a concentration as possible, result in stable readily fluid oil-in-water with a very high proportion of oil. This poses great demands on the emulsifiers used. High shear forces are also to be avoided during emulsification, since in the case of heavy oils there is a danger of an inversion to an extremely highly viscous water-in-oil emulsion. Moreover, the emulsions are to be stable both in regard to higher salinities which occur in many field systems, and in regard to high temperatures. Despite the adequate stability of the emulsions during flow through the pipeline, it should be possible to separate them again as easily as possible.
The emulsifiers proposed so far still do not adequately meet said conditions. In many cases (e.g., U.S. Pat. Nos. 4,285,356, 4,265,264 and 4,249,554), emulsions with oil contents of only 50% are mentioned, which means that for oil transportation half of the pipeline must be sacrificed. In other cases (e.g., Canadian specification Nos. 1,108,205, 1,113,529, 1,117,568, and U.S. Pat. No. 4,246,919), lowering of the viscosity, achieved by addition of emulsifier, is not very great despite the relatively small portion of oil.